Hydraulic system and automatic gearbox

ABSTRACT

The invention relates to a hydraulic system comprising a multi-flow, especially dual-flow, hydraulic pressure supply unit, such as a pump, by which means a volume flow is supplied to a consumer. The invention is characterised in that a valve arrangement is provided for switching between the individual pump flows and/or for interconnecting the individual pump flows.

The invention relates to a hydraulic system with a multi-flow,especially a dual-flow hydraulic pressure supply unit, such as a pump,through which a volume flow is fed to a consumer. The invention alsoconcerns an automatic transmission for motor vehicles.

In modern motor vehicles, hydraulic systems in which at least onepressure supply unit supplies at least one consumer with a definedpressure are being used to improve safety and comfort. The knownhydraulic systems indeed have a high power density, a low power-weightratio and high dynamics, but nonetheless require more energy in relationto regulated electric drives, which leads to higher fuel consumption.Previously mostly single-flow pumps have been used to supply pressureto, for example, automatic transmissions. Single-flow here means thatthe pump conveys one pump flow. In contrast, multi-flow pumps conveyseveral pump flows independently of one another. The pump flows are thusconnected in parallel.

The object of the invention is to reduce the losses in known hydraulicsystems. Here the hydraulic pressure supply unit used in the hydraulicsystem should meet the demands of the automotive industry over a widerange of hydraulic requirements.

The object is accomplished in a hydraulic system with a multi-flow,especially dual-flow, hydraulic pressure supply unit, such as a pump,through which a volume flow is fed to a consumer, in that a valveapparatus for switching between the individual pump flows and/or forinterconnecting the individual pump flows is provided. The valveapparatus enables actuating the individual pump flows selectively. It ispossible as needed to actuate only one or several pump flows with asingle valve apparatus.

A preferred embodiment of the hydraulic system is characterized in thatthe individual pump flows are joined or separated through a stop valve.The stop valve makes it possible to carry away at least one of the pumpflows so that optionally only at least one of the pump flows is conveyedto the consumer.

A further preferred embodiment of the hydraulic system is characterizedin that the at least one pump flow, which is separated by the stop valvefrom the at least one other pump flow, can be carried away through thevalve apparatus. Only one pump flow or several pump flows are suppliedto the consumer as a function of the setting of the valve apparatus. Thestop valve prevents all pump flow from being evacuated.

A further preferred embodiment of the hydraulic system is characterizedin that the valve apparatus comprises a surface pre-stressed by aspring-loaded apparatus, said surface being acted upon with the dynamicpressure of a feedback leading from the consumer to the input side ofthe hydraulic pressure supply unit. The use of the feedback dynamicpressure for actuating the valve apparatus guarantees that the valveapparatus switches from a single-flow to an at least dual-flowconveyance of the hydraulic pressure supply unit when the feedbackdynamic pressure drops below a specified minimum value. If the feedbackdynamic pressure exceeds a specified maximal value, the valve apparatusswitches from an at least dual-flow to an at least single-flowconveyance of the hydraulic pressure supply unit.

A further preferred embodiment of the hydraulic system is characterizedin that a hydraulic resistor is arranged between the valve apparatus andthe input side of the hydraulic pressure supply unit. The hydraulicresistor serves to generate the feedback dynamic pressure for actuatingthe valve apparatus.

A further preferred embodiment of the hydraulic system is characterizedin that the valve apparatus includes a 2/2 way valve that releases aconnection provided between the output side of a pump flow and the inputside of the hydraulic pressure supply unit in the one position, saidconnection being interrupted in the other position of the 2/2 way valve.The 2/2 way valve makes it possible to feed the two pump flows to theconsumer individually or together depending upon need.

A further preferred embodiment of the hydraulic system is characterizedin that the valve apparatus has three shifting stages, whereby in thefirst shifting stage a cooling circuit is not supplied and only one pumpflow is conveyed to the consumer by the hydraulic pressure supply unit,whereby in the second shifting stage the cooling circuit is not suppliedand at least two pump flows are conveyed to the consumer from thehydraulic pressure supply unit, and whereby in the third shifting stage,the cooling circuit is supplied and at least two pump flows are conveyedto the consumer from the hydraulic pressure supply unit. The shiftingstages make it possible to use the valve apparatus, which can beactuated as needed, for also turning the cooling system on and off, forexample a clutch.

A further preferred embodiment of the hydraulic system is characterizedin that the valve apparatus has a further shifting stage in which thecooling circuit is not supplied and a safety valve is activated. Thesafety valve can serve, for example, to prevent overheating of themedium conveyed or represents a redundant opening mechanism for aclutch.

A further preferred embodiment of the hydraulic system is characterizedin that the valve apparatus, especially as a 2/2 way valve, is designedsuch that only one pump flow is conveyed from the hydraulic pressuresupply unit to the consumer as long as a first pressure, especially theadjustment pressure of an automatic transmission, is smaller than orequal to the sum of a second pressure, especially the contact pressureof an automatic transmission, and of a spring force, and in that atleast two pump flows are conveyed from the hydraulic pressure supplyunit to the consumer if the first pressure, especially the adjustmentpressure of an automatic transmission, is greater than the sum of thesecond pressure, especially the contact pressure of an automatictransmission, and of the spring force. In this way, it is guaranteedthat connection of at least one further pump flow will take place as afunction of need.

A further preferred embodiment of the hydraulic system is characterizedin that the valve apparatus includes a tappet whose one face is actedupon with the first pressure and whose other face is acted upon by thesecond pressure and spring force. The tappet moves as a function of theforces acting upon it and thus releases a flow path for one or more pumpflows.

A further preferred embodiment of the hydraulic system is characterizedin that the valve apparatus performs even additional valve functions inaddition to turning on or shutting off the pump flow (=first valvefunction) in that the valve tappet releases or closes openings on othercontrol units. These additional valve functions can, for example, be anapplication of pressure on a hydraulic clutch, or the application ofpressure on the cone pulleys of an infinitely variable transmission. Thecoupling of the first valve function with a further valve functionrepresents a cost advantage because, instead of two slides andboreholes, only one need be manufactured or machined. The coupling ofthe first valve function with a further valve function likewiserepresents a functional advantage if a volume flow requirement isactuated through the further valve function whose coverage takes placein the same valve by turning on a pump flow. The coupling of the firstvalve function with a further valve function likewise represents afunctional advantage when these valve functions can take place inconnection with different motions of the tappet, that is, in partindependently. For example, the additional valve function can representthe application of pressure on a clutch for the second gear, and thetappet now permits connecting an additional pump flow when the clutch isnot activated by a further motion of the tappet. This control andespecially further displacement of the tappet takes place in a knownmanner, for example by applying a small electronically controlledpressure to a face of the tappet.

A further preferred embodiment of the hydraulic system is characterizedin that the valve apparatus includes at least two valves whose switchingrespectively brings about the conveyance of at least one of the pumpflows to the consumer. Both valves in each case assume even furtherfunctions as described above, for example respectively subjecting aclutch to pressure.

A further preferred embodiment of the hydraulic system is characterizedin that the two valves are connected in series. Switching from one ofthe two valves leads to at least one of the pump flows being conveyed tothe consumer. The at least one pump flow is conveyed back to the inputside of the hydraulic pressure supply unit.

A further preferred embodiment of the hydraulic system is characterizedin that a volume flow regulating valve is arranged between the outputside of the pressure supply unit and the consumer. The volume flowregulating valve serves to regulate the volume flow to the consumer. Theexcess volume flow is conveyed back to the input side of the hydraulicpressure supply unit.

A further preferred embodiment of the hydraulic system is characterizedin that connection/disconnection of individual pump flows takes place asneeded. For example, fixed rotational speed thresholds can be defined,at which the switching takes place. Here care should be taken that therequisite need is still being covered when disconnecting a pump flow.

A further preferred embodiment of the hydraulic system is characterizedin that the ratio between the individual pump flows is asymmetrical. Dueto this, it is possible to convey three different volume flows with onehydraulic pressure supply unit.

A further preferred embodiment of the hydraulic system is characterizedin that a first pump flow covers approximately a third and a second pumpflow approximately two thirds of the overall conveyed flow of thehydraulic pressure supply unit. With a corresponding control logic, bothpump flows together can supply 100% or only one pump flow can supply 33or 66% of the entire conveyed flow of the hydraulic supply unit, asneeded.

A further preferred embodiment of the hydraulic system is characterizedin that the hydraulic pressure supply unit includes a vane cell pump oran internal gear wheel pump.

A further preferred embodiment of the hydraulic system is characterizedin that a hydraulic resistor is arranged between the valve apparatus andthe input of the hydraulic pressure supply unit that includes aninjector pump into which the vane cell pump is incorporated. Theinjector pump is used to assure proper filling of the preferablymechanically driven pump at higher rotational speeds.

The indicated objective is accomplished in connection with an automatictransmission for motor vehicles through a previously described hydraulicsystem. The hydraulic system of the invention can also, however, be usedin the steering system or the anti-roll system.

Further advantages, features and details of the invention becomeapparent through the description below, in which various embodiments aredescribed in detail with reference to the drawings. There is shown:

FIG. 1 a hydraulic circuit diagram of a hydraulic system of theinvention for controlling an automatic transmission;

FIG. 2 a block diagram for controlling a dual-flow pump with a valveapparatus and an additional flow regulating valve;

FIG. 3 a block diagram for controlling a dual-flow pump with switchingdependent upon two different pressures;

FIG. 4 a block diagram for controlling a dual-flow pump with a volumeflow conductor and

FIG. 5 a block diagram for controlling a dual-flow pump with two valvesconnected in series.

Contemporary automatic transmissions for passenger cars control thestarting process, the gear ratio change and the activation for thereversing assembly clutch for forward/reverse travel as well as forcooling and lubricating hydraulically. A hydraulic pressure supply unitand a hydraulic control unit are necessary for this.

Up until now, largely single-flow pumps have been used for supplyingpressure to automatic transmissions. The pumps are distinguished in thattheir conveyed volumes are purely proportional to the rotational speed.This is disadvantageous insofar as, in designing pump sizes, oftenextreme situations such as, for example, a rapid adjustment at lowrotational speeds, are decisive for the designs. In many other drivingsituations, the volume flow then made available is not necessary. Theefficiency of these pumps is not optimal since, for example,unnecessarily much hydraulic power is generated by the mechanicallydriven pump at maximum speed. Second, the hydraulic components used,such as, for example, the pump, are e.g. subjected to unnecessarily highstress at maximum speed.

A pump concept is created through the present invention in which therequired volume flow is generated as a function of need. In this way,the hydraulic dissipation power as well as the pump stress can bereduced. With the hydraulic system of the invention, it provesadvantageous that the system pressure can be reduced since at a highsystem pressure leakages as a rule increase. The actuation of theindividual pump flows is preferably conducted such that the net volumeflow remains identical. Generating less volume flow at the samerotational speed with cold oil than with warm oil is desirable since atlow oil temperatures less leakage is present and consequently the volumeflow requirement drops.

It has proven advantageous if a portion of the volume flow madeavailable by the pump is also used for cooling the transmission. Withcold outside temperatures, it is advantageous to reduce the volume flowto the point that only the precisely required amount flows through theradiator and consequently heat losses are reduced. With a very hottransmission, it is advantageous to generate more volume flow thanneeded to increase heat output.

It has likewise proven to be advantageous if a portion of the volumeflow furnished by the pump is also used for cooling individualcomponents of the transmission in danger of overheating, for example,friction clutches. At low friction output, it is advantageous to shutthe volume flow off, while at high friction output (starting on amountain), the required amount of cold oil is poured over the frictionclutch to protect the latter from overheating.

A hydraulic control unit for an automatic transmission with a drivingdisk set 1 and an output disk set 2 is represented in FIG. 1. Thehydraulic system represented in FIG. 1 moreover serves to control aclutch 4 for reverse travel and a clutch 4 for forward travel.Activation of the disk sets 1, 2 and the clutches 4, 5 takes placethrough a pump 8 in which a first pump flow 9 and a second pump flow 10are generated parallel to each other. The two pump flows 9 and 10 arebrought together through a stop valve 12. An additional valve 14 servesto switch between the two pump flows 9, 10 such that either only pumpflow 9 or both the pump flows 9, 10 are conveyed together in thedirection of consumers 1, 2, 4, 5.

A preferred embodiment for selective actuation of two pump flows isrepresented in FIG. 2. One pump 18, a vane cell pump, for example, isconstructed and designed such that a first pump flow 19 is conveyedparallel to a second pump flow 20. The two pump flows 19 and 20 areconnected with each other on the output side of the pump 18 through aconduit 22 in which a stop valve 23 is arranged. The stop valve 23 isarranged in the conduit 22 such that either only the first pump flow 19or, however, the first pump flow 19 as well as the second pump flow 20are conveyed through a conduit 24 to a consumer 25. An orifice plate 26is arranged in the conduit 24 between the output side of the pump 18 andthe consumer 25. The orifice plate 26 belongs, as is indicated through adotted arrow 28, to a flow regulating valve 29, which is arrangedbetween the input side and the output side of the consumer 25 in orderto regulate the volume flow that is supplied to the consumer 25. A 2/2proportional way valve is installed as the flow regulating valve 29. Itthe volume flow conveyed to the consumer 25 exceeds an adjustablemaximum value, then the flow-regulating valve switches into its secondposition from the position represented in FIG. 2. In its second position(not represented), the flow-regulating valve 29 releases a connectionfrom the output side of the pump 18 through the conduit 24 past theconsumer to a feedback conduit 30 that leads to a tank 31.

It is indicated by an arrow 32 that the pressure in the feedback conduit30 serves to control an additional valve apparatus 34. The valveapparatus 34 is a 2/2 proportional way valve that interrupts or releases(not represented) a connecting conduit 35 between the feedback conduit30 and the output side of the second pump flow 20 of the pump 18. Thepressure in the feedback conduit 30 is dammed up in front of the valveapparatus 34 by a hydraulic resistor 36.

With the hydraulic system represented in FIG. 2, the valve apparatus 34is used to convey selectively either only pump flow 19 or the two pumpflows 19 and 20 together to the consumer 25. The back pressure in theconduit 30 is used, as indicated by the arrow 32, to switch the valveapparatus 34 against a spring. The hydraulic fluid volume flow flowingback over the feedback conduit 30 into the tank 31 and/or toward theinput side of the pump 18 meets the hydraulic resistance 36, whichgenerates the back pressure as a function of the volume flow. Theinjector pump used in vane cell pumps can, for example, be used as ahydraulic resistor 36. Such an injector pump is needed in vane cellpumps to assure proper filling of the pump at higher rotational speeds.The hydraulic resistor 36 is represented by a baffle in FIG. 2.

The dual-flow pump 18 is by way of example driven by a crankshaft of aninternal combustion engine and consequently conveys a hydraulic fluidvolume stream as a function of rotational speed. The two pump flows 19and 20 are brought together through the stop valve 23 and are suppliedto the consumer 25 through the conduit 24 by the orifice plate 26 in theposition of the pilot valve 34 represented in FIG. 2. As for theconsumer, it can be, as represented in FIG. 1, a disk set for adjustingthe gear ratios or a clutch in an automatic transmission. Hydraulicfluid flowing back from the consumer 25 through the feedback conduit 30is supplied to the pump 18 again through the hydraulic resistor 36.

If the rotational speed of the pump 18 is increased, then more hydraulicfluid is conveyed and fed to the consumer 25. The return of hydraulicfluid over the feedback conduit 30 to the suction tract of the pump 18is correspondingly higher. The back pressure on the hydraulic resistor36 increasing owing to this leads to the valve apparatus 34shortcircuiting the second pump flow 20 of the pump 18 with theback-flowing hydraulic fluid in the feedback conduit 30. In this way,the pressure of the pump flow 20 declines to the back pressure in thefeedback conduit 30 and closes the stop valve 23. The second pump flow20 of the pump 18 is then switched to recycling and needs only stillconvey against the back pressure in the feedback conduit 30, which wouldbe present in any case. In this way, the output consumption of the pump18 is reduced.

If the rotational speed of the pump 18 and therewith of the volume flowfed to the consumer 25 increases, then the volume flow regulating valve29 in connection with the orifice plate 26 restricts the volume flow tothe consumer 25. The hydraulic system represented in FIG. 2 affords theadvantage that the second pump flow 20 is only added when needed. If theconsumer 25 needs more hydraulic fluid and consequently no or littlehydraulic fluid is being passed back through the flow regulating valve29 and the feedback conduit 30 to the tank 31 or toward the input sideof the pump 18, then the volume flow declines due to the hydraulicresistor 36 and therewith the back pressure in the feedback conduit 30.This causes the valve apparatus 34 to close, and the hydraulic fluidvolume flow of the second pump flow to be conducted back to the consumer25, as represented in FIG. 2. This ensures the increased need forhydraulic fluid. If the need of the consumer 25 declines again, thencorrespondingly more hydraulic oil is fed back, which leads to a renewedswitching of the second pump flow 20 to recycling without pressure.

A cutaway of a hydraulic block diagram is represented in FIG. 3 in whicha valve apparatus for need-dependent volume flow generation isdesignated with 37. The valve apparatus 37 includes a valve housing 38that is connected with the output side of a pump with two pump flows 41and 42 through a conduit 39. The two pump flows 41 and 42 are connectedwith each other through a conduit 45 in which a stop valve 46 isarranged. The fact that the output side of the pump flows 41 and 42 isconnected with a consumer (not represented) is indicated by an arrow 47.The input side of the pump flows 41 and 42 is connected with a hydraulictank 49. A conduit 50 leads from the hydraulic tank 49 to the valvehousing 38. A tappet 52 is pre-stressed against a spring 53 in the valvehousing 38. The face of the tappet 52 facing the spring 53 is acted uponwith a pressure P1. The face of the tappet 52 facing away from thespring 53 is acted upon with a pressure P2.

In the state of the valve apparatus 37 represented in FIG. 3, the pumpflow 42 is conveyed in a circle through the conduit 50 and does notreach the consumer. Only the pump flow 41 reaches the consumer throughconduit 47. It is assured through the stop valve 46 that pump flow 41does not reach the valve housing 38 through conduit 39. When the tappet52 moves such that the conduit 39 is closed, the pressure at the outputof the pump flow 42 rises until the stop valve 46 in the conduit 45releases the connection to the pump flow 41. Then both pump flows 41 and42 are conveyed to the consumer. Connection of the pump flow 42 to pumpflow 41 takes place when the product of a first constant with adjustingpressure P2 is greater than the sum from the product of a secondconstant with the contact pressure P1 and the force of the spring. Thepressures P1 and/or P2 can alternatively be a pressure that controls afunction requiring volume flow already present in the hydraulic controlunit, or a pressure generated by an electric control apparatus by pilotvalve.

The circuit diagram of a hydraulic system is represented in FIG. 4 inwhich a first pump flow 56 as well as a second pump flow 57 of a vanecell pump are fed from a tank 55. The two pump flows 56 and 57 areconnected with each other through a stop valve 58. The output of thefirst pump flow 56 is connected with a valve housing 62 of a valveapparatus 63 through a conduit 60. The second pump flow 57 is connectedwith the valve housing 62 through a conduit 61. A tappet 64 is moveablyaccommodated in the valve housing 62 of the valve apparatus 63. Thetappet can assume even further functions in the region not represented,in that oil channels are closed or opened according to the position ofthe tappet. A connection to a consumer (not represented) is indicated byan arrow 65 that proceeds from the valve housing 62. Moreover a feedbackconduit 66 proceeds from the valve housing 62 and opens into the tank55.

In the position of the tappet 64 represented in FIG. 4, the first pumpflow 56 is conveyed over the conduits 60 and 65 to the consumer. Thesecond pump flow 57 is conveyed back into the tank 55 through conduit 61and the feedback conduit 66. when the tappet 64 is moved to the right,the connection between the conduit 61 and the feedback conduit 66 isinterrupted, which leads to the pressure rising on the output side ofthe second pump flow 57 until the stop valve 58 opens and the two pumpflows 56 and 57 are conveyed together over conduits 60 and 65 to theconsumer.

A circuit diagram of a hydraulic system is represented in FIG. 5 inwhich a first pump flow 71 as well as a second pump flow 72 are fed withhydraulic fluid from a tank 68. The two pump flows 71 and 72 areconnected with each other through a stop valve 73. A conduit toconsumers (not represented) is indicated by an arrow 74. A connectionbetween the output side of the second pump flow 72 to a valve housing 76of a first valve is indicated by an arrow 75. A tappet 77 isaccommodated displaceably in the valve housing 76. The valve housing 76of the first valve is connected with a valve housing 79 of the secondvalve through a conduit 78. A tappet 80 is moveably accommodated in thevalve housing 79 of the second valve. The valve housing 79 of the secondvalve stands in connection with the tank 68 through a feedback conduit81.

Each of the valves represented in the regions not represented on theleft can assume even further functions with the same tappet in that oilchannels are closed or released. For example, clutches can be acted uponby pressure, or in particular consumers requiring volume flow such as acooling system can be switched on.

The second pump flow 72 is conveyed over the conduits 75, 78 and 81 backinto the tank 68, thus in the circuit in the position of the tappets 77and 80 in the associated valve housings 76 and 79 represented in FIG. 5.The connection between the two pump flows 71 and 72 is interrupted bythe stop valve 73. If one of the tappets 77 and 80 is moved to the rightagainst the associated stop, then the feedback into the tank 68 isinterrupted. This leads to a rise in pressure on the output side of thesecond pump flow 72. The pressure on the output side of the second pumpflow 72 rises until the stop valve 73 opens, and both pump flows 71 and72 are jointly conveyed over the conduit 74 to the consumer. The twovalves with valve housings 76 and 79 are thus connected in a row or inseries.

The patent claims submitted with the application are formulationproposals without prejudice to obtaining further-reaching patentprotection. The applicant reserves the right to claim additional featurecombinations previously disclosed only in the description or thedrawings.

References in the dependent claims refer back to the further developmentof the object of the main claim by the features of the respectivedependent claim. They are not to be understood as a waiver of attainingan independent, objective protection for the feature combinations of thereferred back dependent claims.

Since the objects of the dependent claims can form their own andindependent inventions with respect to the state of the art on thepriority day, the applicant reserves the right to make them the objectof independent claims or applications for division. They can furthermorealso contain independent inventions that have an independentconfiguration from the objects of the preceding dependent claims.

The embodiments are not to be understood as a restriction of theinvention. Rather numerous changes and modifications are possible in theframework of the present invention, especially such variants, elementsand combinations and/or materials that can be inferred, for example, bycombination or modification of individual features in combination withthe general description and embodiments as well as features described inthe claims and contained in the drawings or elements and proceduralsteps which can be inferred by the specialist with respect toaccomplishing the objective and lead by combinable features to a newobject or new procedural steps or new procedural step sequences, also tothe extent that they concern manufacturing, testing and operatingprocedures.

1. Hydraulic system with a multi-flow, especially dual-flow hydraulicpressure supply unit, such as a pump, through which a volume flow is fedto a consumer, wherein a valve apparatus for switching between theindividual pump flows and/or for interconnecting the individual pumpflows is provided.
 2. Hydraulic system according to claim 1, wherein theindividual pump flows are led together or separated by a stop valve. 3.Hydraulic system according to claim 2 wherein the at least one pumpflow, which is separated by the stop valve from the at least one otherpump flow, can be carried away through the valve apparatus.
 4. Hydraulicsystem according to claim 3, wherein the valve apparatus has a surfacepre-stressed by a spring-loaded apparatus that is acted upon with theback pressure of a feedback leading from a consumer to the input side ofthe hydraulic pressure supply unit.
 5. Hydraulic system according toclaim 4, wherein a hydraulic resistor is arranged between the valveapparatus and the input side of the hydraulic pressure supply unit. 6.Hydraulic system according to claim 1, wherein the valve apparatus has a2/2 way valve that in the one position releases a connection providedbetween the output side of a pump flow and the input side of thehydraulic pressure supply unit, which is interrupted in the otherposition of the 2/2 way valve.
 7. Hydraulic system according to claim 1,wherein the valve apparatus has three shifting stages whereby in thefirst shifting stage a cooling circuit is not supplied and only a pumpflow is conveyed from the hydraulic pressure supply unit to theconsumer, whereby in the second shifting stage the cooling circuit isnot supplied and at least two pump flows are conveyed from the hydraulicpressure supply unit to the consumer, and whereby in the third shiftingstage, the cooling circuit is supplied and at least two pump flows areconveyed from the hydraulic pressure supply unit to the consumer. 8.Hydraulic system according to claim 7, wherein the valve apparatus has afurther shifting stage in which a safety valve is activated. 9.Hydraulic system according to claim 1, wherein the valve apparatus,especially as a 2/2 way valve, is designed such that only one pump flowis conveyed from the hydraulic pressure supply unit to the consumer aslong as a first pressure, especially the adjusting pressure of anautomatic transmission, is smaller than or equal to the sum of a secondpressure, especially the contact pressure of an automatic transmission,and is a spring force, and wherein at least two pump flows are conveyedfrom the hydraulic pressure supply unit to the consumer if the initialpressure, especially the adjusting pressure of an automatictransmission, is greater than the sum of the second pressure, especiallythe contact pressure of an automatic transmission, and the spring force.10. Hydraulic system according to claim 9, wherein the valve apparatusincludes a tappet whose one face is acted upon with a first pressure andwhose other face is acted upon with the second pressure and the springforce.
 11. Hydraulic system according to claim 1, wherein the valveapparatus includes at least one valve whose switch brings about that atleast one of the pump flows is conveyed to the consumer and assumes anadditional function.
 12. Hydraulic system according to claim 11, whereinat least two valves are connected in series.
 13. Hydraulic systemaccording to claim 1, wherein a volume flow regulating valve is arrangedbetween the output side of the hydraulic pressure supply unit and theconsumer.
 14. Hydraulic system according to claim 1, wherein turning theindividual pump flows on or off takes place dependent upon need. 15.Hydraulic system according to claim 1, characterized in that the ratiobetween the individual pump flows is asymmetrical.
 16. Hydraulic systemaccording to claim 15, wherein a first pump flow comprises approximatelya third and a second pump flows approximately two thirds of the entireconveyed flow of the hydraulic pressure supply unit.
 17. Hydraulicsystem according to claim 1, wherein the hydraulic pressure supply unitincludes a vane cell pump or an internal gear wheel pump.
 18. Hydraulicsystem according to claim 17, wherein a hydraulic resistor is arrangedbetween the valve arrangement and the input side of the hydraulicpressure supply unit which includes an injector pump which isincorporated into the vane cell pump.
 19. Automatic transmission formotor vehicles with a hydraulic system according to claim 1.